如何确保fs.createWriteStream在函数继续执行之前完成； 仅保存一部分图像

Question

I am making a request to an API to get a path to an image. I want to save this image to my database in a mongoDB collection so that the users don't need to constantly make API requests.

I have something set up where I make a request to the imagePath and with the response, I pipe fs.createWriteStream().

Then later on in the code, I use my schema to create a "Character" using this file. It works, but it only saves a fraction of the image, like a top 1/5th. It's not finishing before it continues.

I tried making the function async and then using await before my url request. I have also tried various express/fs methods, like writeFileSync() but those haven't worked.

How do I get the file to finish writing before it does the mongoDB dance?

 let imagePath = req.body.characterObject.thumbnail.path + '.' + req.body.characterObject.thumbnail.extension;

 let superPath = './uploads/marvelousImage.jpg';
let marvelousImage;
  axios({
      url: imagePath,
      responseType: 'stream',
  })
  .then(response => {
      marvelousImage = response.data.pipe(fs.createWriteStream(superPath));

  })
  .catch(err => {
      console.log(err)
  });

    User.findOne({  "username": "administrator"})
    .then(user => {
      let characterId = req.body.characterObject.id;
      for(let i = 0; i < user.characters.length; i++) {
        if(characterId == user.characters[i].id) {
          return Promise.reject({
            code: 422,
            message: 'You already have this character!',
            reason: "CharacterDuplicationError"
          });
        }
      }
      console.log(req.body.characterObject);
      Character.create({
          description: req.body.characterObject.description || 'bocho',
          events: req.body.characterObject.events || 'lopo',
          thumbnail: req.body.characterObject.thumbnail || 'goso',
          name: req.body.characterObject.name || 'John Doe',
          id: req.body.characterObject.id,
          "image.data": fs.readFileSync(superPath),
          "image.contentType": 'image/jpeg'
      })
      .then(char => {
          console.log('lalala');
          console.log(char);
        user.characters.push(char);
        user.save();
        return res.status(201).json({message: "Character Added!"})
      })
    .catch(err => {
        if(err.reason === "CharacterDuplicationError") {
          return res.send(err);
        } 
    })
   })
 });

Answer 1

It isn't clear that this is your only issue here, but it is one of the issues.

In this code:

  .then(response => {
      marvelousImage = response.data.pipe(fs.createWriteStream(superPath));

  })

The promise chain is not waiting for the pipe to finish reading/writing. To do that, you need to return a promise from that .then() handler that resolves when the reading/writing is done. You can do that by listening to events on the writeStream. .pipe() returns the write stream so we can use that return value to set up event handlers and then use those events to resolve/reject a promise that we return. This will make the promise chain wait for the streaming to finish before going to the next .then() in the promise chain.

 .then(response => {
     return new Promise((resolve, reject) => {
         marvelousImage = response.data.pipe(fs.createWriteStream(superPath));
         marvelousImage.on('error', reject).on('close', resolve);
     });
  });

---

Then, I immediately see that you start your database stuff outside of the promise chain. That has to be inside the promise chain.

I attempted to put everything into the promise chain here and flatten the chain and clean up your error handling:

let imagePath = req.body.characterObject.thumbnail.path + '.' + req.body.characterObject.thumbnail.extension;
let superPath = './uploads/marvelousImage.jpg';

axios({
    url: imagePath,
    responseType: 'stream'
}).then(response => {
     return new Promise((resolve, reject) => {
         let marvelousImage = response.data.pipe(fs.createWriteStream(superPath));
         marvelousImage.on('error', reject).on('close', resolve);
     });
}).then(() => {
    return User.findOne({"username": "administrator"});
}).then(user => {
    let characterId = req.body.characterObject.id;
    for (let i = 0; i < user.characters.length; i++) {
        if (characterId == user.characters[i].id) {
            return Promise.reject({
                code: 422,
                message: 'You already have this character!',
                reason: "CharacterDuplicationError"
            });
        }
    }
    console.log(req.body.characterObject);
    return Character.create({
        description: req.body.characterObject.description || 'bocho',
        events: req.body.characterObject.events || 'lopo',
        thumbnail: req.body.characterObject.thumbnail || 'goso',
        name: req.body.characterObject.name || 'John Doe',
        id: req.body.characterObject.id,
        "image.data": fs.readFileSync(superPath),
        "image.contentType": 'image/jpeg'
    });
}).then(char => {
    console.log('lalala');
    console.log(char);
    user.characters.push(char);
    user.save();
    return res.status(201).json({
        message: "Character Added!"
    })
}).catch(err => {
    console.log(err);
    if (err.reason === "CharacterDuplicationError") {
        res.send(err);
    } else {
        res.sendStatus(500);
    }
});